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Backfire Hydrolock
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Author:  deafwish [ Sat Nov 29, 2014 4:48 pm ]
Post subject:  Backfire Hydrolock

Went to start the boat yesterday after being anchored for a couple of hours, when it backfired.
The engine then seemed to have almost seized. I stupidly tried a number of times in desperation.
Upon further inspection and removing some plugs, most pots has salt water in them!
How common is it for a backfire to cause a reverse rotation & suck water in to the engine?
I couldn't get it running again and got an emergency tow.
Back home, I managed to get it running again but the starter now sounds horrible:

http://youtu.be/IOrOKKA_GuQ
<Video> Engine was quickly shut down once started as the hose was not attached.

Engine purrs like a kitten & I'm hoping no internal damage was done.
Oil has no milkiness to it.
Any idea what this nasty starter noise might be?

Author:  fi.na.tine [ Sat Nov 29, 2014 6:53 pm ]
Post subject:  Re: Backfire Hydrolock

Let me start off by saying I am not a pro in the boat mechanics field. However I did find some info that may be of help -
http://www.marinemechanic.com/site/page88.html

Hope it helps.

Author:  deafwish [ Sat Nov 29, 2014 7:41 pm ]
Post subject:  Re: Backfire Hydrolock

Just ran the boat on the hose again. Started first time and runs fine.
Dipstick shows no water, but looking inside the rocker covers is showing a milkshake!
Waaaah! :(

Author:  LouC [ Sat Nov 29, 2014 8:07 pm ]
Post subject:  Re: Backfire Hydrolock

I'd pick up some oil and filters and change it a couple of times. You want the seawater/emulsified water OUT of there as fast as possible. When it backfired, did it seem to diesel (run backwards?) that can definitely suck water up the exhaust. You have a flapper on the exhaust housing, right? Wonder why it backfired?

I still disagree with Volvo's removal of flappers in the Y pipe, for this reason.
Starter, hard to say, but it had to strain to start it against the water, may have worn the Bendix drive. May still work OK though.

Author:  deafwish [ Sun Nov 30, 2014 3:05 pm ]
Post subject:  Re: Backfire Hydrolock

It is hard to say whether it ran backwards at the backfire, or just turned over another half rotation...
Flappers were removed years ago, as per Volvo spec's.
With the starter, how common is it to have damaged the flywheel's teeth gears?
Does the engine need to come out to inspect/ replace the starter and or flywheel?

Author:  LouC [ Sun Nov 30, 2014 4:06 pm ]
Post subject:  Re: Backfire Hydrolock

I'd put those flappers back, in fact I bet OMC parts would fit. I had to replace mine after my bad overheat in the summer before this past.
The starter you should be able to get it out if you have room. Hopefully that damn fiberglass they like to have all around the rear of the engine is not in your way. I'd have to take the old starter and b!tch slap the designer with it if that were the case, lol...
On my boat I remove half the the rear seat, the engine bulkheads and slide the battery back. Then I can get it out in about 20 min.
Two bolts go up thru the bottom of the housing into the block. They were either 5/8ths or 9/16ths. I had to replace the starter (second one) from that same incident because it was full of salt water. Good thing they don't cost much. It's heavy helps to have strong arms, and a long 1/2 drive ratchet. An easy way is to tie a strong line around it and have someone you trust hold the line up above the engine, so you can get the bolts started, without having to hold up the starter with one hand and start the bolts with the other. If you have no helper, then lay a 2x4 across the gunnels, and tie the starter up around it at the right height and maneuver it in place. Necessity is the mother of invention lol....

I doubt any damage happened to the flywheel. At most you might replace the bendix drive. It actually didn't sound that bad to me.
You could bench test it or take it to an auto electric shop and see what they say.

https://www.dropbox.com/s/97y7b927tdgll ... r.jpg?dl=0

Author:  deafwish [ Sun Nov 30, 2014 4:43 pm ]
Post subject:  Re: Backfire Hydrolock

Thanks Lou.
If I re-fitted the flappers, surely there'd be minimal difference given I'd already have 6+ litres of water in the manifolds anyway? :?
I'm trying to get my hands on a compression tester ASAP to see how bad this predicament really is.
If comp' is good, I'll change the oil/ filter and remove the starter for testing.

Author:  LouC [ Sun Nov 30, 2014 8:29 pm ]
Post subject:  Re: Backfire Hydrolock

Deaf, get the salt water/oil mix out NOW, its going to corrode bearings, and other stuff, just like a bad head gasket that leaks coolant into the oil. The comp will only be low if you get rust & pitting on the piston rings and cyl walls.
About where the water came from well you could be right. Its possible for it to get sucked in from the riser itself, (versus it coming up the exhaust from the Y pipe). and Merc actually changed the inner shape of the riser to stop this from happening. They made some clear plastic copies of their standard riser and under certain conditions you could see the water get sucked in from the exhaust stream from the riser.

Does your boat sit low in the water in the stern?

Author:  deafwish [ Mon Dec 01, 2014 12:03 am ]
Post subject:  Re: Backfire Hydrolock

I plan on changing the oil when I check the compression, in about 2 hours.
Yes, my boat sits low in the stern - as would any 18ft boat with a 350 Chevy stern drive in it! :P

Author:  deafwish [ Mon Dec 01, 2014 4:28 am ]
Post subject:  Re: Backfire Hydrolock

Compression test looks promising! 8)

Image

Author:  deafwish [ Mon Dec 01, 2014 5:57 am ]
Post subject:  Re: Backfire Hydrolock

The oil - Not so much! :cry:

Image

Have flushed the crankcase out with 10L of crappy Castrol GTX 20w50 ($9.95 for 5L!) and the milkiness has gone.
Will attempt to remove the starter tomorrow and have it tested. It sounds like marbles in a glass jar when it cranks. :?

Author:  meinmelb [ Mon Dec 01, 2014 6:10 am ]
Post subject:  Re: Backfire Hydrolock

deafwish wrote:
Went to start the boat yesterday after being anchored for a couple of hours, when it backfired.
The engine then seemed to have almost seized. I stupidly tried a number of times in desperation.
Upon further inspection and removing some plugs, most pots has salt water in them!
How common is it for a backfire to cause a reverse rotation & suck water in to the engine?
I couldn't get it running again and got an emergency tow.
Back home, I managed to get it running again but the starter now sounds horrible:

http://youtu.be/IOrOKKA_GuQ
<Video> Engine was quickly shut down once started as the hose was not attached.

Engine purrs like a kitten & I'm hoping no internal damage was done.
Oil has no milkiness to it.
Any idea what this nasty starter noise might be?


Bugger Mate!! Hope there is no damage!

I hydro-locked an Indmar 5.7... might be the same block.. But it was petrol from a stuck injector not salt water. Anyhow pulled the spark plugs, drained the cylinders, new plugs and away it went no harm done. Not sure on your starter motor though..

Fingers crosses mate!!

Author:  deafwish [ Mon Dec 01, 2014 6:30 am ]
Post subject:  Re: Backfire Hydrolock

Cheers Mark.
I'm hoping I can get away with this with only a new starter, but after looking at OEM starters, I can almost buy new heads for that money!!! :shock: :cry:

Author:  LouC [ Mon Dec 01, 2014 9:08 am ]
Post subject:  Re: Backfire Hydrolock

Here in the US you can get an aftermarket starter (Sierra) for about $170 US, see who distributes Sierra parts in Aust. They are part of Teleflex and one of the biggest after market marine companies in the world . No need for a $$$ OE v/p starter. Simple Chevy starter with marine screen to prevent sparks...
I might also ask Hi-Tek about this....the sucking back water...

Also see if your present starter can be repaired. The starter I am using now started acting up a few years ago. Cause was rusty solenoid due to manifold drain above it leaking. Replaced solenoid for $25, kept it for a spare, had installed a new Sierra. Sierra got trashed 3 years later (cooling hose popped off filled bilge with salt water) . Put old starter back in with new solenoid still works fine.

Author:  deafwish [ Tue Dec 02, 2014 3:09 pm ]
Post subject:  Re: Backfire Hydrolock

The starter's out & performs flawlessly on the bench - no horrid metallic noises at all.
I've noticed some very minor wear marks on the flywheel's teeth/ gears & was curious as to whether this could cause the noise?
Is it likely that the bushes, brushes or commutator in the starter have gone bad?
Anything else I can try before I potentially waste hundreds on a new starter?

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